In the liquid developing apparatus of related art, electrostatic latent images formed on the image bearing member are made into visible images by toner, which consists of charged developing particles. Various methods are used to supply the liquid developing agent to the surface of latent images on the image bearing member. For example, a developing roller may be used as the developing agent bearing member, wherein the surface of the roller has depressions and protrusions such that the liquid developing agent is held in the depressions and supplied to the image bearing member. Alternatively, a sponge roller is used as the developing agent bearing member. The sponge roller is pressed against the image bearing member such that the liquid developing agent that has been absorbed by the sponge roller is supplied to the image bearing member. In another method, the image bearing member is immersed in the developing agent tank in which the liquid developing agent is stored such that the liquid developing agent is supplied directly to the image bearing member without use of a developing agent bearing member.
The low-viscosity liquid developing agent usually used in the electrostatic recording and similar apparatus in the related art consists of IsoparG (registered trademark of the Exxon Corporation), an organic solvent, in which toner is mixed at a proportion of about 1 to 2%. It is desirable to use a more highly concentrated liquid developing agent than that used in the apparatus of the related art and to reduce the volatility of the solvent to allow production of a safer and smaller liquid developing apparatus, but this type of apparatus cannot be found in the related art. Moreover, the ideal method of supplying liquid developing agent to the latent image surface on the image bearing member when using a highly concentrated and highly viscous liquid developing agent (a liquid developing agent with a high viscosity of 100 to 10,000 mPa.s in which toner is dispersed at high concentrations in the non-conductive liquid) which adheres more strongly to the image bearing member was heretofore unknown.